Pulsed substantially single-mode fiber lasers emitting multiple kW peak powers with average powers in the 10-20 W range are ideal laser sources for many of today's applications in material processing such as, for example, marking and engraving. Such fiber-based devices have numerous advantages over other types of lasers, such as flexible pulse durations/repetition rates, compact air cooled platforms due to the high efficiency operation, and maintenance-free operation. There is a particular interest in linearly polarized single-mode pulsed fiber devices with a similar set of generic specifications. Non-polarized single-mode pulsed fiber lasers in the 10-20 W average power regime have been successfully demonstrated. See, for example, A. Piper, A. Malinowski, K. Furusawa, D. J. Richardson “1.2 mJ, 37 ns single-moded pulses at 10 kHz repetition rate from a Q-switched ytterbium fiber laser” in CLEO proceedings, CMK3, San-Francisco, Calif., USA, 2004).
However, developing high-power linearly polarized single-mode pulsed devices can be challenging due to management of the fiber non-linearities, coupled with polarization control in the large mode area (LMA) fibers often used to generate high peak powers. In addition, producing pulses at 10-20 kW peak powers with spectrally narrow linewidth, which can be very useful for efficient conversion to visible and UV wavelengths through frequency doubling/tripling can be very challenging. See, for example, C. Ye, M. Gong, P. Yan, Q. Liu and G. Chen, “Linearly-polarized single-transverse-mode high-energy multi-ten nanosecond fiber amplifier with 50 W average power”, Optics Express, 14, 17, 7604, (2006).
Certain methods are known from the literature based on seeded fiber amplifiers. See, for example, the above noted paper by Ye et al., where the seed source is a diode pumped solid state laser (DPSSL). As another example, see F. Di Teodoro, J. P. Koplow, S. W. Moore, D. A. V. Kliner, “Diffraction-limited, 300-kW peak-power pulses from a coiled multimode fiber amplifier, Optics Letters, 27, 7, 518, (2002), where the seed source comprises a passively Q-switched microchip laser. Another approach is based on diode sources. See, for example, D. Creeden, J. McCarthy, R. Day, P. Ketteridge, E. Chicklis, “Near diffraction-limited, 1064 nm, all-fiber master oscillator fiber amplifier (MOFA) with enhanced SRS suppression for pulsed nanosecond applications”, SSDLTR Technical Digest 2006, Paper FIBER 1-4. See also W. Torruellas, Y. Chen, B. McIntosh, J. Farroni, K. Tankala, S. Webster, D. Hagan, M. Soileau, M. Messerly, J. Dawson, “High peak power Yb-doped fiber amplifiers”, Fiber Lasers III: Technology, Systems, and Applications, Proc. SPIE Vol. 6102, 61020N (2006). Other approaches are based on CW fiber lasers that are subsequently modulated, such as disclosed in A. Liu, M. Noesen and R. Mead, “60 W green output by frequency doubling of a polarized Yb-doped fiber laser”, Optics Letters, 30, 1, 76, (2005). These approaches, however, can suffer from the need to fiber couple the output from the solid state laser into the fiber power amplifier stage. The foregoing approaches also usually deliver low peak power from the seed laser and subsequently require multiple (two or three) fiber amplifier stages to generate the ˜20 kW peak power targeted for these applications.
It is an object of the present invention to address one or more of the drawbacks and disadvantages of the prior art.